Method of registering a blank substrate to a pattern generating particle beam apparatus and of correcting alignment during pattern generation

ABSTRACT

We have developed a method of registration of a particle beam to internal alignment targets present within photoresist areas which are to be imaged. The method does not affect the photoresist, so the quality of pattern produced in the resist after imaging is not affected. The method used for registration of the particle beam to internal alignment targets also can be used to align a pattern in real time, while the pattern is being created, with the internal alignment targets. The real time alignment during creation of a pattern image in the photoresist can be used to correct for drift, or thermal expansion, or gravitational sag, by way of example.

FIELD OF THE INVENTION

In general, the present invention relates to a method of registering ablank substrate, including non-exposed photoresist, to a patterngenerating particle beam apparatus. The invention also relates to thecorrection of alignment of a pattern being generated to a plannedpattern which is to be generated on the blank substrate. The particlebeam may be an electron beam, an ion beam, a proton beam, a neutronbeam, an X-ray, or a laser by way of example. It is understood that alaser beam may not be considered to be a particle beam in someapplications; however, for purposes of the present application, when aparticle beam is referred to, “particle beam” includes lasers. Theinvention is useful for semiconductor manufacturing in general, and isparticularly useful in the production of a lithographic mask (reticle)of the kind used to pattern substrates in the semiconductor industry.

BRIEF DESCRIPTION OF THE BACKGROUND ART

A method which has typically been used to register a particle beam to aphotoresist-coated blank substrate or to an existing pattern employs useof the particle beam itself. This approach typically utilizes aback-scatter detector, where particles that experience high-anglescattering events with the target are collected. The particle beam isscanned in a raster pattern over an alignment target, and a back-scatter“image” is generated from the detector signal, where the brightness ofeach pixel is determined by the number of particles striking thedetector in a time period corresponding to that pixel. Thisself-alignment method is limited by poor contrast with respect to noise.Further, to avoid incidental exposure of a photoresist-coated blanksubstrate, the alignment targets must be placed outside of the portionsof the photoresist which are to be imaged.

When the substrate is a lithographic mask, and the particle beam iscomprised of electrons, in a region of a mask covered with chrome,relatively few back-scattered electrons result from the chrome, becausethe chrome is thin and the scattering cross-section is small, owing tothe high electron beam energy. Many more back-scattered electrons resultfrom the underlying silicon dioxide (and other oxides) present in themask structure, because the silicon dioxide portion of the structure isvery thick compared to the chrome layer (about 50,000 times thicker).Consequently, a target area where no chrome is present scatters nearlyas many electrons as a region where chrome is present. As a result, useof this technique to determine whether a pattern which is being createdis in alignment with alignment targets present inside an area ofphotomask which is being imaged is difficult, since the back-scatterimage of the targets typically provides poor contrast which makesdetermining of a centroid location of an alignment target difficult.Further, use of an alignment target which is present in an area ofphotoresist which is being imaged causes exposure of the photoresist,and the pattern which is generated suffers.

When the particle beam used to create the pattern is an electron beam,another problem is the thermal expansion of the substrate duringcreation of the pattern. This makes it difficult to register an electronbeam to write a pattern in a proper relationship to a planned patternalignment on the substrate, using the electron beam itself as areference. U.S. Pat. No. 6,424,879 to Chilese et al., issued Jul. 23,2002, describes an electron beam writing system which includes anelectron beam patterning machine operable to emit an electron beam toform a pattern on a substrate. A computer control system, coupled to theelectron beam patterning machine, has a plurality of pre-computeddistortion maps. Each distortion map describes expected distortions ofthe substrate caused by exposure of the substrate to the electron beam.The computer control system controls the electron beam patterningmachine using the distortion maps in order to adjust for the expecteddistortions. The invention makes use of one or more pre-computeddistortion maps which describe the thermal and/or mechanical responsesof a substrate to electron beam patterning. The distortion maps areused, in conjunction with pattern writing data, to determine thedistortions expected in a patterning process, so that adjustments can bemade. Because the distortion maps are pre-computed, the computationaltime required to calculate the thermal distortions is significantlyreduced.

The concept of correcting for distortions which will occur duringwriting of an image on a substrate based on data obtained during writingof that same image on an equivalent substrate at an earlier time is alsodiscussed in U.S. Pat. No. 6,833,158 issued to Sandstrom et al. on Apr.19, 2005. In particular, the invention is said to relate to a method anda system for predicting and correcting geometrical errors in lithographyusing masks, such as large-area photomasks or reticles, and exposurestations, such as wafer steppers or projection aligners. The methodcomprises the steps of collecting information about a mask substrate,mask writer, an exposure station, and/or about behavior of a processingstep that will occur after the writing of the mask. Further the methodcomprises predicting, from the combined information, distortions whichwill occur in the pattern when it is subsequently printed on theworkpiece; calculating from the prediction a correction to diminish thepredicted distortion, and exposing the pattern onto the mask substratewhile applying the correction for the predicted distortions.

Fabrication of a semiconductor device or a photomask/reticle is acomplicated process involving a number of interrelated steps whichaffect the feature placements or the critical dimensions of variouspatterns produced. Whether the feature placements or the criticaldimensions at issue are those of patterns on a semiconductor wafer, orthose of patterns on a reticle used to pattern a semiconductor wafer,the semiconductor device may not meet specification if related patternsof materials on multiple layers within the device are not properlyaligned. An ability to adjust the alignment of a newly forming patternrelative to alignment targets present inside an area of substrate to bepatterned permits compensation for changing process conditions duringimaging of the pattern in a photoresist. This makes it possible tocorrect for drift, thermal expansion, or gravitational sag, for example,during imaging of the photoresist, whether the process is directsemiconductor device manufacturing or reticle (photomask) fabrication.The reproducibility of the manufacturing process itself may be improved,including the process window. Process window refers to the amountprocess conditions can be varied without having a detrimental outcome onthe product produced. The larger the processing window, the greaterchange permitted in processing conditions without a detrimental affecton the product. Thus, the ability to adjust a pattern alignment to atarget present in an area of pattern formation, during that patternformation is especially valuable in terms of processing window. Abroader processing window generally results in a higher yield ofin-specification product produced.

It would be highly desirable to be able to use internal patternalignment targets which are present within areas of a substrate whichare to be patterned. It would also be desirable to be able toperiodically reassess the relative geometrical locations of a patternbeing formed relative to internal alignment targets, so that moreprecise corrections can be made for drift, thermal expansion,gravitational sag, or other changes which affect the alignment of aforming pattern (an, image in a photoresist, for example) duringfabrication.

SUMMARY OF THE INVENTION

We have developed a method of registration of a particle beam tointernal alignment targets present within unexposed photoresist areaswhich are to be imaged. The method does not affect the photoresist, sothe quality of pattern produced in the resist after imaging is notaffected. The method of registration also makes it possible to align apattern which is being developed in the photoresist during the creationof the pattern by the particle beam. The method makes use of a positionfiducial which can be accurately measured by an optical reader (such asan electron microscope); pattern alignment targets which are presentwithin a photoresist area which is to be pattern imaged; and, a particlebeam which can measure the same position fiducial and generate a patternin the photoresist. The registration of the particle beam to internalalignment targets present within photoresist areas on a blank(non-imaged) substrate is achieved using the position fiducial locationin combination with vectors which indicate the location path of theinternal alignment targets present within the photoresist areas.Registration of the particle beam with the internal alignment targetsperiodically, during creation of the particle-beam-generated pattern,continually provides an improvement in the overall alignment of thepattern being created to the with the planned geometrical pattern layouton the substrate. Often the improved alignment is the result of acorrection for drift, or thermal expansion, or gravitational sag, or acombination these, which is occurring during creation of the pattern bythe particle beam.

To avoid affecting the photoresist by the registration and alignmentprocesses, the position fiducial is scanned/imaged by an optical reader,followed by scanning/imaging of the pattern alignment targets by anoptical reader. Locational coordinates for the position fiducial and thepattern alignment targets are calculated, and vectors from the positionfiducial to each pattern alignment target are also calculated.Subsequently, the particle beam is used to scan/image the positionfiducial. Coordinates are calculated for the particle beam axis. Thecoordinates for the particle beam axis are used in combination with thelocational vectors which were measured by the optical reader withrespect to the pattern alignment targets, to register the patternalignment targets to the particle beam axis. The position fiducial is ata fixed position relative to the substrate and to the pattern alignmenttargets present on the substrate. The registration of a given plannedpattern alignment target to the position fiducial, and the registrationof a given point location on a pattern which is being created by theparticle beam to the position fiducial may be determined in a matter ofseconds. At least 3 pattern alignment target positions must bedetermined for registration, and additional pattern alignment targetsneed to be determined to measure distortion. Typically use of at least 8pattern alignment target positions is recommended for distortionmeasurement, to assist in alignment of a pattern which is being createdby the particle beam. A “real time” assessment of the distortionsbetween the planned pattern and the pattern which is being created canbe made in seconds or minutes, where comparisons of more than threeoptical reader imaging of pattern alignment target locations are made. Areal time alignment adjustment of the particle beam being used to createthe pattern provides a continual improvement in the overall alignment ofthe pattern being created to the planned pattern locations on thesubstrate. An excellent embodiment for use of this technology is in thefabrication of photomask/reticles of the kind used for semiconductorproduction.

An optical microscope provides higher contrast to noise than theelectron beam backscattering method of determining location which wasdescribed in the background art. Under the right conditions, greaterthan 75% of incident light will reflect (and be detected by an opticalcamera) from a layer of chrome of the kind which is used in thefabrication of reticles, where less than 5% of incident light will bereflected from exposed silicon dioxide regions, for example. Inpractice, the contrast will depend on the specifics of the substrate andthe optics involved, including the illumination. One of skill in the artwill be able to envision applications of the method to a variety ofsubstrates, which are considered to be included within the method of theinvention. The higher contrast-to noise makes determining the positionof the alignment target more accurate.

The use of a position fiducial that can be accurately measured by bothan optical microscope and an electron-beam, for example, typicallyemploys a transmission feature fabricated into a semiconductor or metal.This fiducial acts to bridge the independent coordinate systems measuredat either the optical microscope or the particle beam. As a consequence,the knowledge of the relative positions of the particle beam column andoptical microscope becomes unimportant. The drift between the opticalmicroscope and the particle beam column does not matter because vectorsare used as a coordinating system to retain pattern alignments. Further,alignment marks can be placed inside active areas of a photoresist usedto fabricate a device or within photoresist active areas duringfabrication of a semiconductor device or a reticle/photomask, sinceappropriate optical illumination will not expose a photoresist which issensitive to particle beam radiation.

An apparatus which may be used to align a substrate having a non-imaged(blank) photoresist on its surface to a particle beam axis used togenerate a pattern image in the photoresist comprises:

a primary beam optical axis in the form of a particle beam axis, whichparticle beam is used to generate a pattern;

a secondary optical axis in the form of an optical reader such as anoptical microscope;

a position fiducial (also referred to as a grid), which is located at astationary position relative to the substrate; and

a controller/computer adapted to control the operation of the particlebeam and the optical microscope axis, where the controller/computer isalso adapted to calculate at least three vectors from the positionfiducial to at least three alignment target locations on a substrateusing data input from the secondary optical axis, and wherein thecontroller coordinates the at least three vectors with a location of theposition fiducial measured by the primary optical axis to conform theprimary beam optical axis to an alignment with respect to the alignmenttarget locations on the substrate.

The apparatus is useful in registering a blank photoresist-coveredsubstrate with a particle beam, and is useful in aligning a patternbeing created by the particle beam with pattern alignment targetspresent on the substrate during writing of a planned pattern on thesubstrate using a particle beam.

The use of three alignment target locations permits registration of theprimary optical axis relative to the blank photoresist-coated substrate.However, for alignment of the pattern which is being created by theparticle beam with alignment target locations on the substrate (wheresuch alignment target locations may be within the area to be patterned),the use of three alignment target locations does not provide anydistortion information. Each additional alignment target locationdetermined as a part of the process improves the distortion informationavailable. Typically about 8 to about 16 alignment target locationsprovides helpful distortion information. Often the fabrication processitself limits the number of alignment target locations which can bemeasured. In terms of timing for real time alignment and correction ofthe location of the primary optical axis during pattern writing, thelarger the number of measurements which need to be made, the longer thetime period required, and this creates a limitation in itself.Typically, the coarse locations of alignment targets with respect to theposition fiducial on a substrate are known to better than the field ofview of the optical microscope, so that the precise locations of thealignment targets can be determined without first searching for thetargets. For purposes of this invention, any method may be used todetermine the coarse locations of the alignment targets, for example,precision mechanical alignment of the substrate with respect to theposition fiducial, a second optical microscope with a larger field ofview (which typically exhibits poorer location accuracy), or tilingseveral optical microscope images together to create a composite imageover a larger extent (area) than a single field of view.

We have developed a method of registering a particle beam axis relativeto a blank, unexposed photoresist covered substrate, where at least aportion of the registration targets are present within an area of theblank photoresist which is to be imaged, comprising;

-   -   a) providing a primary beam optical axis in the form of a        particle beam axis, wherein said particle beam is used to        generate a pattern;    -   b) providing a secondary optical axis in the form of an optical        reader axis;    -   c) providing a position fiducial at a fixed location relative to        the substrate (often the position fiducial is located on the        substrate stage);    -   d) providing a controller adapted to control the operation of        the particle beam axis and the optical microscope axis, wherein        the controller is also adapted to calculate a plurality of        vectors from the position fiducial to a plurality of pattern        alignment targets present on the substrate;    -   e) using the secondary optical axis to determine a feature (such        as a centroid) location of the position fiducial, and        calculating coordinates x₀ y₀ of the feature location;    -   f) moving the substrate under the secondary optical axis such        that an alignment target is within a field of view of the        secondary optical axis, and calculating coordinates x₁ y₁ of the        alignment target location;    -   g) calculating an alignment vector for the alignment target,        which vector is l₁ =(x₁−x₀)x+(y₁−y₀)y;    -   h) calculating at least 2 additional alignment vectors for at        least 2 additional alignment target locations using steps f) and        g);    -   i) moving the position fiducial under the primary beam optical        axis, and scanning a feature (such as a centroid) using the        primary beam optical axis in a manner to determine the location        of the position fiducial;    -   j) calculating coordinates (x′₀, y′₀) of the position fiducial        for the primary beam optical axis;    -   k) calculating a location for previously-determined alignment        target locations on the substrate with respect to the primary        beam optical axis, by applying corresponding location vectors        l_(n), where n is an integer of at least three, to the        coordinates (x′₀, y′₀) which represent a starting location of        the primary optical axis, whereby the primary optical axis is        registered to the pattern alignment targets on the blank        photoresist coated substrate.

Typically, when pattern alignment targets ranging from 3 to about 16 innumber are used, the time period required for registration ranges fromabout 10 seconds to about 60 seconds, respectively.

We have also developed a method of aligning a plannedparticle-beam-generated pattern to pattern alignment targets, wherein atleast a portion of the pattern alignment targets are present within anarea of the substrate which includes non-exposed photorseist, duringwriting of the planned pattern by the particle beam. The methodcomprises:

-   -   a) providing a primary beam optical axis in the form of a        particle beam axis;    -   b) providing a secondary optical axis in the form of an optical        reader axis;    -   c) providing a position fiducial at a fixed location relative to        the substrate (often the position fiducial is located on the        substrate stage);    -   d) providing a controller adapted to control the operation of        the particle beam axis and the optical microscope axis, wherein        the controller is also adapted to calculate a plurality of        vectors from the position fiducial to a plurality of pattern        alignment targets present on the substrate;    -   e) using the secondary optical axis to determine a feature (such        as a centroid) location of the position fiducial, and        calculating coordinates x₀ y₀ of the feature location;    -   f) moving the substrate under the secondary optical axis such        that an alignment target is within a field of view of the        secondary optical axis, and calculating coordinates x₁ y₁ of the        alignment target location;    -   g) calculating an alignment vector for the alignment target,        which vector is l₁, =(x₁−x₀)x+(y₁−y₀)y;    -   h) calculating at least 2 additional alignment vectors for at        least 2 additional alignment target locations using steps f) and        g);    -   i) moving the position fiducial under the primary beam optical        axis, and scanning a particle beam from the primary beam optical        axis in a manner to determine a feature (such as a centroid)        location of the position fiducial;    -   j) calculating coordinates (x′₀, y′₀) of the position fiducial        for the primary beam optical axis;    -   k) calculating a location for previously-determined alignment        target locations on the substrate by applying corresponding        location vectors l_(n), where n is an integer ranging from 3 to        about 16, to the coordinates (x′₀, y′₀) which represent a        starting location of the primary optical axis; and    -   l) using a plurality of alignment target locations relative to a        location of the primary beam optical axis to conform the primary        beam optical axis to an alignment with respect to the alignment        target locations during writing of a particle-beam-generated        pattern on the substrate.

Additional coordinate transforms may be applied to known coordinates (inthe primary optical axis coordinate space) with respect to alignmenttarget locations of the pre-existing pattern on the substrate, tocorrect for scale, orthogonality, or other errors which may becomeapparent during writing of a new electron-beam-generated pattern on thesubstrate containing a pre-existing pattern.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustration of one embodiment of a lay out of apparatuswhich can be used to carry out the invention.

FIG. 2 shows the use of a secondary optical axis 206, such as an opticalmicroscope, to develop a relationship between a position fiducial 204and the coordinates of alignment target locations, 208-220, for example,of a planned pattern to be written on a substrate, where therelationship includes the determination of vectors, where each vectorrepresents a path between the position fiducial 204 and an alignmenttarget location.

FIG. 3 shows the use of a secondary optical axis 306, as described withrespect to optical axis 206 of FIG. 2, to develop a relationship betweena position fiducial 304 and alignment target locations, 308-322, forexample, of a planned pattern to be written on a substrate.Subsequently, a primary optical axis 366, such as a particle beam axis,is used in combination with the position fiducial 304 and vectorspreviously determined for the alignment target locations using thesecondary optical axis, first to register the particle beam to thetarget locations 368-382, and subsequently to align a pattern as it isbeing created by the particle beam with changed target locations (notshown) if there is a change in target locations due to drift, orsubstrate expansion, or substrate sag, for example, during writing ofthe planned pattern.

DETAILED DESCRIPTION OF THE INVENTION

As a preface to the detailed description, it should be noted that, asused in this specification and the appended claims, the singular forms“a”, “an”, and “the” include plural referents, unless the contextclearly dictates otherwise.

Use of the term “about” herein indicates that the named variable mayvary to ±10%.

A substantial improvement has been achieved in registration of aparticle beam to a substrate including a blank (non-imaged) photomask,where alignment targets are used as a means of registration. Previouslyalignment targets were located at the periphery of the substrate soimaging/scanning of the alignment targets would not affect the area ofthe photoresist to be imaged during patterning of the photoresist. Inthe present method, the alignment targets used to register the particlebeam to the substrate can be located within the areas of the substratewhere photoresist to be patterned is present. A position fiducial whichcan be accurately measured by both an optical microscope and a particlebeam axis and at least three alignment targets, at least a portion ofwhich are located within areas of the substrate where photoresist is tobe patterned, are used to provide the registration.

In addition, the method which is used to register the alignment targetsto the particle beam can also be used to provide a real time alignmentof a pattern being created by the particle beam with alignment targetson the substrate.

EXAMPLES Example One

FIG. 1 is a schematic drawing which shows an embodiment of the apparatus100 which may be used to carry out the invention. The substrate 106 onwhich a pre-existing pattern (not shown) was created is positioned upona substrate stage 102. The substrate stage also includes a positionfiducial 104 which is in a fixed position relative to substrate 106. Anoptical reader, in the form of an optical microscope 108, including anoptical axis 110 is used to scan a position fiducial 104, typicallylocated on substrate stage 102, and alignment targets (not shown)located upon a blank photoresist-coated substrate 106. The scanned datafor alignment target locations (not shown) on the blankphotoresist-coated substrate 106 are recorded in imager 112 which is aCMOS camera or CCD camera, for example, and (typically digital) data issent from imager 112 to a controller/computer 118, which calculatescoordinates for the alignment target locations and also calculatesvectors from the position fiducial 104 to each alignment targetlocation.

With further reference to FIG. 1, the apparatus 100 also includes aparticle beam apparatus 114, having an axis 116 which is used to scanthe position fiducial 104 initially, and then is used subsequently tocreate a pattern on the substrate 106. In FIG. 1, the particle beamapparatus 114 is an electron beam. The electron beam collects currentthat is not blocked by the grid/position fiducial. The electron beam ismuch smaller than the position fiducial, so most of the time the currentis either transmitted or blocked, with edges transmitting fractions. Thecurrent transmission data is digitalized and sent to controller/computer118. The controller/computer 118 uses the particle beam 114 scanned datafrom position fiducial 104 in combination with the vectors calculatedfrom the optical microscope 108 data to determine the alignment targetlocations of the pre-existing pattern on the substrate relative to theparticle beam 114 axis 116.

Coordinates for the location of alignment target locations (not shown)on substrate 106 relative to the location of the particle beam 114 axis116 are calculated using the controller/computer 118. Thecontroller/computer 118 is programmed to create a planned pattern whichis to be aligned with the alignment targets present on the substrate106. At the beginning, the creation of a planned pattern is based on thecoordinates for the location of the pattern alignment target locationsdetermined by the optical microscope 108 prior to initiation of theplanned pattern creation. As pattern creation proceeds on substrate 106,the optical microscope is again scanned over the position fiducial 104and over the pattern alignment locations, to provide an adjustedlocation for the pattern alignment target locations relative to positionfiducial 104. The electron beam 114 axis 116 is also scanned overposition fiducial 104, and new coordinates for the location of patternfeature alignment target locations on the substrate 106 relative to thelocation of particle beam 114 axis 116 are determined. The controllerthen calculates any correction to the location at which the new patternshould be created and adjusts the particle beam 114 axis 116 toimplement this correction.

The controller/computer 118 referenced above may be any one of a numberof controllers of the kind used in the art of registration and alignmentin the semiconductor industry.

As previously mentioned, by selecting a photoresist which is notaffected by the optical process used to measure the location of thepattern feature alignment targets, it is possible to accumulateregistration and alignment information without affecting the creation ofthe new pattern which is to be aligned with the pre-existing pattern ona substrate.

Example Two

FIG. 2 illustrates the initial registration of pre-existing patternalignment targets 208, 210, 212, 214, 216, 218, 220 present on asubstrate 202, using an optical microscope 206. A position fiducial 204which is in a fixed position relative to substrate 202 was scanned andimaged by an optical reader, in this case optical microscope 206, whilethe stage (not shown) was at stage position “A” relative to substrate202 and position fiducial 204. Coordinates (x₀, y₀) for a centroid ofposition fiducial 204 were determined. The stage (not shown) was thenmover to position “B” so that optical microscope 206 was at the positionshown on FIG. 2 relative to substrate 202 and position fiducial 204. Thecoordinates (x_(n), y_(n)) were then determined for a nominal number ofpre-existing pattern alignment targets, such as 208, 210, 212, 214, 216,218, and 220. The minimum number of pattern alignment targets which maybe used for registration is three. Typically about 10 pattern alignmenttargets are used to get a registration of the alignment targets to theoptical microscope 206. Additional pattern alignment targets provideadditional information, which improves the accuracy of the registration.Further, when the pattern alignment targets are used to align a patternwith a planned pattern geometrical lay out, during creation of thepattern using a particle beam, an increased number of pattern alignmenttargets provides an improved picture of distortion in the substrateduring creation of the pattern. This permits correction of the patternfor such distortions during writing of the pattern. Registration ofadditional pattern alignment targets require additional time formeasurement, and this places limitations on the measurement process. Upto 16 additional pattern alignment targets have been used duringphotomask/reticle pattern creation, since this is a process whichprogresses at a speed which permits time for the use of this number ofpattern alignment targets. Typically, about 2 seconds are required toregister an individual pattern alignment target to the positionfiducial.

In FIG. 2, the stage positions “A” and “B” show how the centroidposition of the position fiducial 204 was determined using opticalmicroscope 206 at stage position “A”, and then the stage was moved toplace optical microscope 206 over a pre-existing pattern alignmenttarget 220, which was scanned and imaged by optical microscope 206 and acentroid for the pattern alignment feature target 220 was determined.The imaging of pattern alignment target 220 was done at the first ofseveral stage positions within the general stage position “B”. It is notnecessary that the precise dimensions of the pattern at location 220 bedetermined, but only that the centroid of a feature at that location bedetermined. At this centroid location, coordinates (x₂₂₀, y₂₂₀) weredetermined. The stage was then moved to place optical microscope 206over another pattern alignment feature target 216, at a second locationwithin general stage position “B”, where the centroid for the patternalignment feature target 216 was determined. Coordinates (x₂₁₆, y₂₁₆)were calculated. This process was carried out a number of times, toprovide coordinates for the centroids of other pre-existing patternalignment target such as 208, 210, 212, 214, or 218, by way of example.A location vector l₂₂₀, which extends from position fiducial (x₀,y₀) topattern alignment feature target 220 was calculated by thecomputer/controller 118 illustrated with respect to FIG. 1. A locationvector l₂₁₆, which extends from position fiducial (x₀,y₀) to patternalignment feature target 216 was calculated by the computer/controller118. The other location vectors were also calculated as well. Once allof the desired location vectors were calculated, the new pattern (notshown) was created to be in alignment with the pre-existing patternpresent on substrate 202.

As discussed above, the centroids of the various pre-existing patternfeature alignment targets may be re-measured relative to the positionfiducial 204 during the process of writing a pattern. This is necessaryif changes in substrate 202 affect the location of the pre-existingpattern feature alignment targets and the location vectors which areused for alignment of the pattern which is being created requirecorrection.

Example Three

FIG. 3 illustrates the manner in which a relationship between theparticle beam axis and the pre-existing pattern feature alignmenttargets is developed. Periodic reassessment of this relationship duringwriting of a pattern with the particle beam enables continual alignmentof the pattern which is being created with the planned patterngeometrical lay out on the substrate. Schematic 300 of the methodelements and system includes an optical section 301 and a particle beamsection 303. The optical section 301 mirrors the illustration in FIG. 2.Initial registration of pre-existing pattern alignment targets 308, 310,312, 314, 316, 318, 320, 322, and 324 present on a substrate 302, theoptics image of the pre-existing pattern, is accomplished using anoptical reader 306 such as an optical microscope. The imaging ofposition fiducial 304, which is in a stationary relationship withrespect to substrate 302, was carried out when the substrate stage wasat position “A” relative to optical reader 306. The optical reader 306,with the substrate stage at position “A” scans the position fiducial 304and determines a location for a particular feature location for theposition fiducial, and the scanned data is used to calculate positionfiducial 304 feature coordinates, typically a centroid coordinate (x₀,y₀). The substrate stage (not shown) is then moved to one of a number ofpositions within general stage position “B”. The optical reader 306 at afirst location within general stage position “B” over the substrate 302may determine feature coordinates for a first pre-existing patternalignment target such as 322, for example. The substrate stage is thenmoved to a second location within general stage position “B” todetermine feature coordinates for a second pre-existing patternalignment target such as 320, for example. The optical reader 306 isused to image a number of pre-existing pattern alignment targets, andthe data is sent to a controller/computer such as 118 shown in FIG. 1,for calculation of coordinates. The pattern alignment targets areselected to be at locations on the pre-existing pattern which areconsidered to be the most useful in determining whether patterndistortion of the pre-existing pattern is occurring during formation ofa pattern on the blank photoresist-coated substrate. In schematic 300,optical section 301, the coordinates (x_(n), y_(n)) are determined for anominal number of pattern alignment target features, such as 308, 310,312, 314, 316, 318, 320, 322, and 324, for example and not by way oflimitation. As previously mentioned, typically about 10 patternalignment targets are used, so that there is a good indication ofdistortion which is taking place during writing of a pattern. Up to 16additional pattern alignment targets have been used duringphotomask/reticle pattern creation, since this is a process whichprogresses at a speed which permits time for the use of this number ofpattern alignment targets.

The movement from position fiducial 304 to a pattern alignment targetfeature follows a vector l_(n). A location vector is calculated for eachpattern alignment target feature, for example, location vector l₃₀₈extends from position fiducial coordinates (x₀,y₀) to pattern alignmentfeature target 308 coordinates (x₃₀₈,y₃₀₈); location vector l₃₁₀ extendsfrom position fiducial coordinates (x₀,y₀) to pattern alignment featuretarget 310 coordinates (x₃₁₀,y₃₁₀); and so on. This initial set ofposition alignment vectors is used in combination with the positionfiducial coordinates to provide an initial registration of plannedpattern locations on the substrate.

The obtaining of an initial registration of the pre-existing patternwith respect to the particle beam 366 is shown in schematic 300 particlebeam section 303. With the substrate stage at position “C”, the particlebeam 366 was used to scan and image position fiducial 304, inputtingdata into the controller/computer 118 for calculation of the positionfiducial coordinates (x′₀,y′₀). The location vectors l₃₃₈, l₃₄₀, l₃₄₂,l₃₄₄, l₃₄₆, l₃₄₈, l₃₅₀, l₃₅₂, and l₃₅₄, for example, for the patternalignment features determined using the optical reader, were then usedin combination with the particle beam 366 data for the position fiducial304, to provide particle beam location vectors l₃₆₈, l₃₇₀, l₃₇₂, l₃₇₄,l₃₇₆, l₃₇₈, l₃₈₀, l₃₈₂, and l₃₈₄for the location of pattern alignmentfeatures 308, 310, 312, 314, 316, 318, 320, 322, and 324, with respectto the axis of particle beam 366, for example. A combination of theparticle beam 366 position fiducial 304 coordinates (x′₀,y′₀) with theparticle beam location vectors l₃₆₈, l₃₇₀, l₃₇₂, l₃₇₄, l₃₇₆, l₃₇₈, l₃₈₀,l₃₈₂, and l₃₈₄ registers the substrate and planned pattern to be writtenwithin the particle beam coordinates system. The pattern which is beingcreated while the substrate stage is moved within general stage position“D” can then be aligned with the pattern alignment targets, illustratedas features 308, 310, 312, 314, 316, 318, 320, 322, and 324, forexample, on the substrate 302. Since it takes only seconds to scan theposition fiducial and an individual pattern alignment target featureusing the optical reader 306, to scan the position fiducial with theparticle beam, and to convert the vectors from optical readercoordinates to particle beam coordinates, a continual updating of thelocation of pattern alignment features on the substrate with thelocation of the axis of the particle beam may be carried out. Thiscontinual updating of the alignment between the pre-existing pattern andthe particle beam writing the pattern permits a more accurate alignmentof the pattern as it is created. Errors in alignment which would havebeen present due to factors such as drift, or thermal expansion, orgravitational sag, or a combination thereof, can be substantiallyreduced if not eliminated altogether.

While the invention has been described in detail above with reference toparticular schematics and drawings, various modifications within thescope and spirit of the invention will be apparent to those of workingskill in this technological field. One skilled in the art, upon readingapplicants' disclosure, can make use of various particle beams andregistration and alignment hardware and software known in the art totake advantage of the invention disclosed. Accordingly, the scope of theinvention should be measured by the appended claims.

1. A method of improving registration of a particle-beam relative to anon-exposed, photoresist-coated substrate, wherein at least a portion ofthe registration targets are present within an area of the non-exposedphotoresist which is to be imaged during patterning, said methodcomprising: a) providing a primary beam optical axis in the form of aparticle beam axis, wherein said particle beam is used to generate apattern; b) providing a secondary optical axis in the form of an opticalreader axis; c) providing a position fiducial at a fixed locationrelative to the substrate; d) providing a controller adapted to controlthe operation of the particle beam axis and the optical microscope axis,wherein the controller is also adapted to calculate a plurality ofvectors from the position fiducial to a plurality of pattern alignmenttargets present on the substrate; e) using the secondary optical axis todetermine a feature location of the position fiducial, and calculatingcoordinates x₀ y₀ of the feature location; f) moving the substrate underthe secondary optical axis such that an alignment target is within afield of view of the secondary optical axis, and calculating coordinatesx₁ y₁ of the alignment target location; g) calculating an alignmentvector for the alignment target, which vector is l₁=(x₁−x₀)x+(y₁−y₀)y;h) calculating at least 2 additional alignment vectors for at least 2additional alignment target locations-using steps f) and g); i) movingthe position fiducial under the primary beam optical axis, and scanninga feature of said position fiducial using the primary beam optical axisin a manner to determine the location of the position fiducial; j)calculating coordinates (x′₀, y′₀) of the position fiducial for theprimary beam optical axis; and k) calculating a location forpreviously-determined alignment target locations on the substrate withrespect to the primary beam optical axis, by applying correspondinglocation vectors l_(n), where n is an integer of at least three, to thecoordinates (x′₀, y′₀) which represent a starting location of theprimary optical axis, whereby the primary optical axis is registered tothe pattern alignment targets on the non-imaged photoresist coatedsubstrate.
 2. A method in accordance with claim 1, wherein said particlebeam is selected from the group consisting of an electron beam, an ionbeam, a laser beam, a proton beam, a neutron beam, or an X-ray.
 3. Amethod in accordance with claim 1 or claim 2, wherein said registrationof said particle beam relative to a non-imaged, photoresist-coatedsubstrate is carried out using a number of pattern alignment targetsranging from about 3 targets to about 16 targets.
 4. A method inaccordance with claim 3, wherein said registration of said particle beamis carried out over a time period ranging between about 10 seconds andabout 60 seconds.
 5. A method in accordance with claim 1, wherein acontroller/computer is used to calculate at least three alignmentvectors corresponding to the relationship between the position fiducialcoordinates and pattern alignment targets measured using the secondaryoptical axis, and to relate the particle beam to the pattern alignmenttargets using a combination of the data related to said coordinates ofthe position fiduciary for said primary beam optical axis in combinationwith the at least three alignment vectors.
 6. A method of aligning aplanned particle-beam-generated pattern to pattern alignment targets,wherein at least a portion of said alignment targets are present withinan area of said substrate which includes non-exposed photorseist, duringwriting of said planned pattern by said particle beam, comprising: a)providing a primary beam optical axis in the form of a particle beamaxis; b) providing a secondary optical axis in the form of an opticalreader axis; c) providing a position fiducial at a fixed locationrelative to said substrate; d) providing a controller adapted to controlthe operation of said particle beam axis and said optical microscopeaxis, wherein the controller is also adapted to calculate a plurality ofvectors from said position fiducial to at least three pattern alignmenttargets present on said substrate; e) using said secondary optical axisto determine a feature location of said position fiducial, andcalculating coordinates x₀ y₀ of said feature location; f) moving thesubstrate under the secondary optical axis such that an alignment targetis within a field of view of said secondary optical axis, andcalculating coordinates x₁ y₁ of said alignment target location; g)calculating an alignment vector for said alignment target, which vectoris l₁=(x₁−x₀)x+(y₁−y₀)y; h) calculating at least 2 additional alignmentvectors for at least 2 additional alignment target locations using stepsf) and g); i) moving said position fiducial under the primary beamoptical axis, and scanning a particle beam from said primary beamoptical axis in a manner to determine a feature location of saidposition fiducial; j) calculating coordinates (x′₀, y′₀) of saidposition fiducial for said primary beam optical axis; k) calculating alocation for alignment target locations on said substrate whichlocations were previously determined using said secondary optical axisby applying corresponding location vectors l_(n), where n is an integerranging from 3 to about 16, to the coordinates (x′₀, y′₀) whichrepresent a starting location of said primary optical axis; and l) usinga plurality of alignment target locations relative to a location of saidprimary beam optical axis to conform said primary beam optical axis toan alignment with respect to said alignment target locations duringwriting of a particle-beam-generated pattern on said substrate.
 7. Amethod in accordance with claim 6, wherein said particle beam isselected from the group consisting of an electron beam, an ion beam, alaser beam, a proton beam, a neutron beam, or an X-ray.
 8. A method inaccordance with claim 7, wherein said particle beam is an electron beam,and wherein a coordinate transform is applied to known coordinates in acoordinate space of said primary beam optical axis, with respect toalignment target locations on said substrate, to correct for scale,orthogonality, or other errors which become apparent during writing ofan electron-beam-generated pattern on said substrate.
 9. An apparatuswhich used to align a substrate having a non-imaged photoresist on itssurface to a particle beam axis used to generate a pattern image in thephotoresist comprising: a primary beam optical axis in the form of aparticle beam axis, which particle beam is used to generate a pattern; asecondary optical axis in the form of an optical reader such as anoptical microscope; a position fiducial, which is located at astationary position relative to said substrate; and acontroller/computer adapted to control the operation of said particlebeam and said optical microscope axis, where said controller/computer isalso adapted to calculate at least three vectors from said positionfiducial to at least three alignment target locations on a substrateusing data input from said secondary optical axis, and wherein thecontroller coordinates the at least three vectors with a location ofsaid position fiducial measured by the primary optical axis to conformsaid primary beam optical axis to an alignment with respect to saidalignment target locations on said substrate.
 10. An apparatus inaccordance with claim 9, wherein said particle beam is selected from thegroup consisting of an electron beam, an ion beam, a laser beam, aproton beam, a neutron beam, or an X-ray.
 11. An apparatus in accordancewith claim 9, wherein said position fiducial is present on a stage onwhich said substrate is mounted.
 12. An apparatus in accordance withclaim 9, wherein said position fiducial is present in a form of a grid.